The present invention is directed to auxiliary drive apparatus which can be operated manually for use with other driving assemblies, such as valve actuators, requiring very high thrust loads, for example up to 40,000 pounds.
There have been a number of auxiliary or override drive apparatus proposed for use with normally powered driving assemblies.
For example, U.S. Pat. No. 4,080,844 illustrates a manual control apparatus; however, this apparatus cannot obtain the thrust needed for heavy duty applications without drastic design changes. In addition, the length of the stem and hence movement of the shaft in this patent is limited because the shaft cannot run through the body at its top.
U.S. Pat. No. 4,114,469 discloses an auxiliary valve actuator in which the gears are in engagement at all times and are not disengageable.
U.S. Pat. No. 3,842,690 illustrates an automatically disengageable manual control, in which the drive nut is not free to float and the shaft is rotated rather than driven axially.
U.S. Pat. No. 3,667,730, discloses a quick-action jack which does have a declutchable nut; however, the shaft must be turned to move it and thrust can be exerted in one direction only rather than in both directions.
The apparatus of the above patents in general are not suitable for auxiliary driving, such as manual driving, of a shaft axially in both directions under high thrust loads of up to and in excess of 40,000 pounds, in which movement of the stem or shaft is not limited, and in which the shaft can be engaged and driven in any position.